Whenever there is a mention of automotive lubricants, we come across the word ‘additives’. Even the oil manufacturers merit their oils by using terms like ” most advanced additives”, “high-quality additives”, “extreme wear additives”, “best motor oil additives”, etc. So what are these additives? Let’s find out. 

add engine oil

Engine oil additives are chemical compounds that improve the lubricant performance of base oil – also known as the base stock. Nearly all automotive lubricants contain additives; they range between 0.1 to 30 % of the base oil volume. The additional percentage (%) depends upon the specific application. Different combinations of additives are used in gear oils, Bike Engine Oils, Car Engine oils, Agriculture machinery oils and transmission oils and hydraulic oil. 

These additives are added to base stock to enhance existing properties, suppress undesirable properties and add new properties. Below are some of the most common additives that are distributed based on these three roles.

Additives that enhance base oil properties
  • Antioxidants: When the lubricant comes in contact with oxygen and heat, it reacts with the hydrocarbons in the former to form carboxylic acids and sludge. While carboxylic acid produces corrosion, sludge formation causes surface deposits and viscosity to increase. Antioxidants or oxidation inhibitors prolong the above-mentioned process and extend the life of the lubricant.
rusty nuts and bolts
  • Rust and Corrosion Inhibitors: The metal parts of the engine tend to catch rust and develop corrosion. The rust and corrosion inhibitors protect these metal parts by neutralizing acids and creating a protective film on their surface that repels moisture. These inhibitors are used in most lubricants. Some inhibitors protect specific metals only. Therefore, a combination of inhibitors is used in the oil.
  • Antifoam agents: Sometimes air gets mixed up in the oil, turning it into a frothy, foamy substance with reduced efficiency. Antifoam agents prevent the formation of air bubbles and foam into the oil.
  • Demulsifiers: When lubricants are exposed to steam or water, they form a stable oil-water mixture. This mixture is also known as Emulsion. Demulsifier additives change the interfacial tension of the oil so that water separates from the oil and is drained off at a reservoir with ease.
Additives that suppress undesirable base oil properties
  • Viscosity Index Improvers:  Oil tends to thin out as temperature rises and thicken as the temperature falls. Viscosity index (VI) improvers are polymer additives that keep oil stable at extreme temperatures. These additives are used extensively in the manufacturing of multi-grade oils.
  • Pour-point depressants: At low temperatures, wax crystals form in paraffinic mineral oils crystallize and obstruct oil from flowing freely. Pour-point depressants dissolve these wax formations and enable lubricant to flow at low temperatures or Pour-point. 
Additives that add new properties to the base oil  
  • Extreme pressure (EP) additives: These additives bond with the metal to create a strong film that prevents the friction created by metal-to-metal contact. EP additives keep the engine friction-free at high loads and high contact temperatures.
  • Metal Deactivators: Metal deactivators prevent the metal from causing the oil to be oxidized by creating a film on metal surfaces.
  • Detergents: Detergents a.k.a Alkaline additives prevent oil impurities like sludge from depositing on the metal surfaces. They are also used to neutralise the harmful acids that form in the oil.  
How Oil Additives Get Depleted

Additives are sacrificial and get depleted due to decomposition, absorption (into the metal), and separation due to settling or filtration. With each day of oil usage, the additives in it become less effective. If the oil is not changed, then viscosity increases, sludge and corrosive acids begin to form. All this will lead to increased wear and tear of the engine. 

After a certain period of use, an oil change is recommended. If the oil is of good quality, then the additives function for longer. Use the best engine oil to keep your engine healthy.